Effect of Mn2+ doping on the lattice and the microwave dielectric properties of MgTa2O6 ceramics

A series of Mn²⁺-doped Mg_1-xMn_xTa₂O₆ (x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ceramics were synthesized by solid-state reaction method. The influence of introducing Mn–O bonds as a partial replacement for Mg–O bonds on the lattice and microwave dielectric properties was systematically investigated. XRD and Rietveld refinement confirm that Mn²⁺ occupies the 2a Wyckoff position and forms a pure trirutile phase. Moreover, based on the chemical bond theory, the dielectric constant is mainly affected by the ionicity of the Ta–O bond. The lattice and dielectric properties remain relatively stable with Mn²⁺ doping below 0.1, but excessive Mn²⁺ doping leads to pronounced distortion of the lattice, which is not beneficial for lattice stability and microwave dielectric properties. Introducing an appropriate amount of Mn–O bonds with high bond dissociation energy facilitates MgO6 octahedron stability, which improves the thermal stability of the lattice. Accordingly, the microwave dielectric properties for 0.06 Mn²⁺-doped MgTa₂O₆ ceramics were determined: ε_r = 28, Q × f = 105,000 GHz (at 7.5 GHz), τ_f = 19.5 ppm/^°C.     

我国中空吹塑行业发展现状及“十四五”期间重点产品、工艺和设备发展方向

从原料、中空成型机和吹塑工艺等方面介绍了我国中空吹塑行业发展现状，并对电子化学品专用超洁净桶、高压储氢四型瓶、全电动中空成型机、微发泡中空成型技术和挤吹聚对苯二甲酸乙二醇酯（PET）容器等在“十四五”期间的重点产品、工艺和设备发展方向进行了展望。     

ADS实验大厅中子防护工程技术研究

为了保障加速器驱动次临界系统(ADS)散裂靶与反应堆耦合特性及影响验证实验的顺利进行,以原子能院现有的临界实验装置为基础,对堆厅部分墙体进行屏蔽改造。建造由聚乙烯、镉、铅、钢以及混凝土等材料构成的屏蔽装置,以防止临界装置产生的射线外泄,使工作人员受到的照射保持在合理水平。通过MCNP模拟计算,完成了屏蔽结构的优化设计。基于槽钢支撑结构、铅屏蔽层、镉屏蔽层和聚乙烯屏蔽层等材料组成的组合屏蔽结构建立简化模型,采用ANSYS有限元分析程序计算分析得出各部分应力小于许用应力,稳定性符合要求。最后通过工程实践,完成对屏蔽性能理论计算结果的验证。     

The digital public humanities: giving new arguments and new ways to argue

ABSTRACT

In response to the latest “crisis” in the humanities, advocates have marched, rallied, fundraised, and—especially—argued. This essay contends that communication scholars can support the growing “case for the humanities” by analyzing argumentative strategies, and more specifically, by offering ethical argumentative strategies that avoid replicating structures of domination. In particular, we look to Mari Lee Mifsud's theorization of rhetoric as gift, which follows Henry W. Johnstone in conceptualizing argument as something other than winning over an adversary. We place Mifsud's theorization of the gift in conversation with the methods of the digital public humanities (DPH), which acknowledge and offer abundant resources for meaning-making. Through the methods of DPH, we offer a response to the humanities “crisis” that activates the humanities’ already broad constituencies by giving resources for humanistic inquiry rather than seeking to capture adversaries. Our case study is Photogrammar, a DPH project for organizing, searching, and visualizing the New Deal and World War II era photographs funded by the U.S. federal government. The project forefronts visual, nonlinear, and interactive argumentation in order to engage publics in generative humanistic inquiry. By enlisting participants and sharing expertise, Photogrammar shows how humanities advocates can deepen attachments to the humanities and build broad constituencies of collaborators and allies.     

Quasi-static compressive behaviour of aluminium cenosphere syntactic foams

In this paper, cenosphere particles embedded in AA2014 aluminium matrix are used to fabricate syntactic foam by stir casting method. The particle size is about 100?µm and foam density is about 1990?kg?m^?3. Compression tests at strain rate 0.001/s are performed on foam samples to characterise their mechanical properties which are then used in numerical analysis on commercial finite element analysis software ABAQUS/CAE with isotropic elastic-plastic material model. Experimental and numerical results show good conformity in deformation behaviour with elastic and plateau zones showing average deviations less than 5% and 20%, respectively. Foams showed high yield stress and energy absorption capabilities that can be useful in making blast and impact resistant structures.     

On the buckling properties of concentric carbon/boron-nitride multi-walled nanotubes: A finite element investigation

Finite element modeling approach is used here to investigate the behavior of concentric multi-walled boron-nitride and carbon nanotubes under the compressive loadings. Double-walled and triple-walled concentric boron-nitride and carbon nanotubes with different arrangements and geometries are considered. It is shown that multi-walled boron-nitride nanotubes lose their stabilities at larger compressive forces than other arrangements in which at least one carbon wall exists. Comparing the armchair and zig-zag multi-walled nanotubes, the latter one has larger buckling force than the former one. It is also shown that the nanotubes with smaller radii have larger critical compressive forces than those with larger radii.     

Enhancing optical absorption in visible light of ZnO co-doped with europium and promethium by first-principles study through modified Becke and Johnson potential scheme

By using first-principles calculations we studied the electronic, optical and magnetic properties of ZnO co-doped with Eu and Pm. In this calculation, we used Wien2k code based on full potential linearized augmented plane waves (FP-LAPW) method with the modified Becke-Johnson (mBJ) approximation. This correction gives good band gap compared to experimental band gap. The introduction of Eu and Pm codoping leads to an increase in the band gap. Electrons can transit easily from the valence band to the conduction band, which results in an enhancement of visible light absorption in a wider absorption range. Absorption spectra reach a high value in visible and infrared light regions. With the significance of the obtained results, the studied compounds may potentially find spintronic and optoelectronic applications.     

能源土边界面模型的应力更新算法及算例分析

水合物的存在会显著影响能源土的刚度、峰值强度与剪胀性。针对已有能源土模型的不足，结合边界面模型的建模思想，构建一个新的能源土边界面模型，模型参数较少，能够恰当反映能源土的应力-应变关系。计算能源土变形问题的核心在于正确积分塑性本构方程，应用完全隐式回退Euler算法，建立模型应力及塑性内变量的更新公式，并给出显式的一致性切线模量表达式。基于ABAQUS软件提供的二次开发接口，编写模型的用户材料子程序，应用已有试验数据验证程序正确性。最后应用开发的子程序对能源土的平面应变试验进行模拟，分析水合物饱和度对剪切带倾角与孔隙比的影响。     

Unconditional stability and error estimates of the modified characteristics FEMs for the time-dependent incompressible MHD equations

This paper focuses on the unconditional stability and convergence of characteristics type methods for the time-dependent incompressible MHD equations. For this purpose, we introduce a new characteristics time-discrete system. The optimal error estimates in $L^2$ and $H^1$ norms for the typical modified characteristics finite element method unconditionally can be deduced, while the whole previous works require certain time-step restrictions. Some numerical experiments document performance of the characteristics type methods for the time-dependent incompressible MHD equations.